Abstract:

The transmission has a plurality of members that can be utilized in
powertrains to provide eight forward speed ratios and one reverse speed
ratio. The transmission includes three planetary gear sets, six
torque-transmitting devices, one fixed interconnection and a grounded
member. The powertrain includes an engine and torque converter that is
continuously connected to one of the planetary gear members and an output
member that is continuously connected with another one of the planetary
gear members. The six torque-transmitting devices provide
interconnections between various gear members, and the transmission
housing, and are operated in combinations of three to establish eight
forward speed ratios and one reverse speed ratio.

Claims:

1. A multi-speed transmission comprising:an input member;an output
member;first, second and third planetary gear sets each having first,
second and third members;an interconnecting member continuously
connecting said third member of said first planetary gear set with said
second member of said second planetary gear set;said first member of said
first planetary gear set being continuously connected with a stationary
member;six torque-transmitting devices for selectively interconnecting
said members of said planetary gear sets with said stationary member or
with other members of said planetary gear sets, said six
torque-transmitting devices being engaged in combinations of three to
establish at least eight forward speed ratios and at least one reverse
speed ratio between said input member and said output member;wherein a
first of said six torque-transmitting devices is operable for selectively
connecting said second member of said third planetary gear set with said
stationary member;wherein a second of said six torque-transmitting
devices is operable for selectively connecting said second member of said
first planetary gear set with said second member of said third planetary
gear set;wherein a third of said six torque-transmitting devices is
operable for selectively connecting said second member of said first
planetary gear set with said first member of said third planetary gear
set; andwherein a fourth of said six torque-transmitting devices is
operable for selectively connecting said third member of said first
planetary gear set with said first member of said third planetary gear
set.

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. The transmission of claim 1, wherein a fifth of said six
torque-transmitting devices is operable for selectively connecting said
first member of said second planetary gear set with said second member of
said third planetary gear set.

7. The transmission of claim 6, wherein a sixth of said six
torque-transmitting devices is operable for selectively connecting said
third member of said second planetary gear set with said first member of
said third planetary gear set.

9. The transmission of claim 1, wherein said first, second and third
members of said first, second and third planetary gear sets comprise a
sun gear member, a planet carrier assembly member and a ring gear member,
respectively.

10. The transmission of claim 1, wherein said input member is continuously
connected with said first member of said second planetary gear set, and
said output member is continuously connected with said third member of
said third planetary gear set.

11. (canceled)

12. (canceled)

13. (canceled)

14. A multi-speed transmission comprising:an input member;an output
member;first, second and third planetary gear sets each having first,
second and third members;an interconnecting member continuously
connecting said third member of said first planetary gear set with said
second member of said second planetary gear set;said first member of said
first planetary gear set being continuously connected with a stationary
member;six torque-transmitting devices for selectively interconnecting
said members of said planetary gear sets with said stationary member or
with other members of said planetary gear sets, said six
torque-transmitting devices being engaged in combinations of three to
establish at least eight forward speed ratios and at least one reverse
speed ratio between said input member and said output member; andwherein
said input member is continuously connected with said first member of
said second planetary gear set, and said output member is continuously
connected with said third member of said third planetary gear set.

15. A multi-speed transmission comprising:an input member;an output
member;first, second and third planetary gear sets each having first,
second and third members;an interconnecting member continuously
connecting said third member of said first planetary gear set with said
second member of said second planetary gear set;said first member of said
first planetary gear set being continuously connected with a stationary
member;six torque-transmitting devices for selectively interconnecting
said members of said planetary gear sets with said stationary member or
with other members of said planetary gear sets, said six
torque-transmitting devices being engaged in combinations of three to
establish at least eight forward speed ratios and at least one reverse
speed ratio between said input member and said output member;wherein a
third of said six torque-transmitting devices is operable for selectively
connecting said second member of said first planetary gear set with said
first member of said third planetary gear set; andwherein said first,
second and third members of said first, second and third planetary gear
sets comprise a sun gear member, a planet carrier assembly member and a
ring gear member, respectively.

16. The transmission of claim 7, wherein said input member is continuously
connected with said first member of said second planetary gear set, and
said output member is continuously connected with said third member of
said third planetary gear set.

17. The transmission of claim 16, wherein said first, second and third
members of said first, second and third planetary gear sets comprise a
sun gear member, a planet carrier assembly member and a ring gear member,
respectively.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a power transmission having three
planetary gear sets that are controlled by six torque-transmitting
devices to provide eight forward speed ratios and one reverse speed
ratio.

BACKGROUND OF THE INVENTION

[0002]Passenger vehicles include a powertrain that is comprised of an
engine, multi-speed transmission, and a differential or final drive. The
multi-speed transmission increases the overall operating range of the
vehicle by permitting the engine to operate through its torque range a
number of times. The number of forward speed ratios that are available in
the transmission determines the number of times the engine torque range
is repeated. Early automatic transmissions had two speed ranges. This
severely limited the overall speed range of the vehicle and therefore
required a relatively large engine that could produce a wide speed and
torque range. This resulted in the engine operating at a specific fuel
consumption point during cruising, other than the most efficient point.
Therefore, manually-shifted (countershaft transmissions) were the most
popular.

[0003]With the advent of three- and four-speed automatic transmissions,
the automatic shifting (planetary gear) transmission increased in
popularity with the motoring public. These transmissions improved the
operating performance and fuel economy of the vehicle. The increased
number of speed ratios reduces the step size between ratios and therefore
improves the shift quality of the transmission by making the ratio
interchanges substantially imperceptible to the operator under normal
vehicle acceleration.

[0004]Six-speed transmissions offer several advantages over four- and
five-speed transmissions, including improved vehicle acceleration and
improved fuel economy. While many trucks employ power transmissions
having six or more forward speed ratios, passenger cars are still
manufactured with three- and four-speed automatic transmissions and
relatively few five or six-speed devices due to the size and complexity
of these transmissions.

[0005]Seven-, eight- and nine-speed transmissions provide further
improvements in acceleration and fuel economy over six-speed
transmissions. However, like the six-speed transmissions discussed above,
the development of seven-, eight- and nine-speed transmissions has been
precluded because of complexity, size and cost.

SUMMARY OF THE INVENTION

[0006]It is an object of the present invention to provide an improved
transmission having three planetary gear sets controlled to provide eight
forward speed ratios and one reverse speed ratio.

[0007]The transmission family of the present invention has three planetary
gear sets, each of which includes a first, second and third member, which
members may comprise a sun gear, a ring gear, or a planet carrier
assembly member, in any order.

[0008]In referring to the first, second and third gear sets in this
description and in the claims, these sets may be counted "first" to
"third" in any order in the drawing (i.e., left to right, right to left,
etc.). Additionally, the first, second or third members of each gear set
may be counted "first" to "third" in any order in the drawing (i.e., top
to bottom, bottom to top, etc.) for each gear set.

[0009]Each carrier member can be either a single-pinion carrier member
(simple) or a double-pinion carrier member (compound). Embodiments with
long pinions are also possible.

[0010]An interconnecting member continuously connects the third member of
the first planetary gear set with the second member of the second
planetary gear set.

[0011]The first member of the first planetary gear set is continuously
connected to a stationary member (transmission housing/casing). The input
member is continuously connected with the first member of the second
planetary gear set. The output member is continuously interconnected with
the third member of the third planetary gear set.

[0012]A first torque-transmitting device, such a brake, selectively
connects the second member of the third planetary gear set with a
stationary member (transmission housing/casing).

[0013]A second torque-transmitting device, such as a clutch, selectively
connects the second member of the first planetary gear set with the
second member of the third planetary gear set.

[0014]A third torque-transmitting device, such as a clutch, selectively
connects the second member of the first planetary gear set with the first
member of the third planetary gear set.

[0015]A fourth torque-transmitting device, such as a clutch, selectively
connects the third member of the first planetary gear set with the first
member of the third planetary gear set.

[0016]A fifth torque-transmitting device, such as a clutch, selectively
connects the first member of the second planetary gear set with the
second member of the third planetary gear set.

[0017]A sixth torque-transmitting device, such as a clutch, selectively
connects the third member of the second planetary gear set with the first
member of the third planetary gear set.

[0018]The six torque-transmitting devices are selectively engageable in
combinations of three to yield eight forward speed ratios and one reverse
speed ratio.

[0019]A variety of speed ratios and ratio spreads can be realized by
suitably selecting the tooth ratios of the planetary gear sets.

[0020]The above features and other features and advantages of the present
invention are readily apparent from the following detailed description of
the best modes for carrying out the invention when taken in connection
with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

[0021]FIG. 1a is a schematic representation of a powertrain including a
planetary transmission in accordance with the present invention;

[0022]FIG. 1b is a truth table and chart depicting some of the operating
characteristics of the powertrain shown in FIG. 1a; and

[0023]FIG. 1c is a schematic representation of the powertrain of FIG. 1a
depicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024]Referring to the drawings, there is shown in FIG. 1a a powertrain 10
having a conventional engine and torque converter 12, a planetary
transmission 14, and a conventional final drive mechanism 16. The engine
12 may be powered using various types of fuel to improve the efficiency
and fuel economy of a particular application. Such fuels may include, for
example, gasoline; diesel; ethanol; dimethyl ether; etc.

[0025]The planetary transmission 14 includes an input member 17
continuously connected with the engine 12, a planetary gear arrangement
18, and an output member 19 continuously connected with the final drive
mechanism 16. The planetary gear arrangement 18 includes three planetary
gear sets 20, 30 and 40.

[0026]The planetary gear set 20 includes a sun gear member 22, a ring gear
member 24, and a planet carrier assembly member 26. The planet carrier
assembly member 26 includes a plurality of pinion gears 27 rotatably
mounted on a carrier member 29 and disposed in meshing relationship with
both the sun gear member 22 and the ring gear member 24.

[0027]The planetary gear set 30 includes a sun gear members 32, a ring
gear member 34, and a planet carrier assembly member 36. The planet
carrier assembly member 36 includes a plurality of pinion gears 37
rotatably mounted on a carrier member 39 and disposed in meshing
relationship with both the sun gear members 32 and the ring gear member
34.

[0028]The planetary gear set 40 includes a sun gear member 42, a ring gear
member 44, and a planet carrier assembly member 46. The planet carrier
assembly member 46 includes a plurality of pinion gears 47 mounted on a
carrier member 49 and disposed in meshing relationship with both the ring
gear member 44 and the sun gear member 42.

[0030]The input member 17 is continuously connected with the sun gear
member 32 of the planetary gear set 30. The output member 19 is
continuously connected with the ring gear member 44 of the planetary gear
set 40. The sun gear member 22 of the planetary gear set 20 is
continuously connected with the transmission housing 60.

[0031]An interconnecting member 70 continuously connects the ring gear
member 24 of the planetary gear set 20 with the planet carrier assembly
member 36 of the planetary gear set 30.

[0032]A first torque-transmitting device, such as brake 50, selectively
connects the planet carrier assembly member 46 of the planetary gear set
40 with the transmission housing 60. A second torque-transmitting device,
such as clutch 52, selectively connects the planet carrier assembly
member 26 of the planetary gear set 20 with the planet carrier assembly
member 46 of the planetary gear set 40. A third torque-transmitting
device, such as clutch 54, selectively connects the planet carrier
assembly member 26 of the planetary gear set 20 with the sun gear member
42 of the planetary gear set 40. A fourth torque-transmitting device,
such as clutch 55, selectively connects the ring gear member 24 of the
planetary gear set 20 and the planet carrier assembly member 36 of the
planetary gear set 30 via interconnecting member 70 with the sun gear
member 42 of the planetary gear set 40. A fifth torque-transmitting
device, such as clutch 56, selectively connects the sun gear member 32 of
the planetary gear set 30 with the planet carrier assembly member 46 of
the planetary gear set 40. A sixth torque-transmitting device, such as
clutch 57, selectively connects ring gear member 34 of the planetary gear
set 30 with the sun gear member 42 of the planetary gear set 40.

[0033]As shown in FIG. 1b, and in particular the truth table disclosed
therein, the torque-transmitting devices are selectively engaged in
combinations of three to provide eight forward speed ratios and one
reverse speed ratio, all with single transition shifts with a double
overdrive.

[0034]As set forth above, the engagement schedule for the
torque-transmitting devices is shown in the truth table of FIG. 1b. The
chart of FIG. 1b describes the ratio steps that are attained in the above
described transmission. For example, the step ratio between the first and
second forward speed ratios is 1.72, while the step ratio between the
reverse speed ratio and first forward ratio is -0.45.

[0035]Referring to FIG. 1c, the embodiment of powertrain 10 depicted in
FIG. 1a is illustrated in a lever diagram format. A lever diagram is a
schematic representation of the components of a mechanical device such as
an automatic transmission. Each individual lever represents a planetary
gearset, wherein the three basic mechanical components of the planetary
gear are each represented by a node. Therefore, a single lever contains
three nodes: one for the sun gear member, one for the planet gear carrier
member, and one for the ring gear member. The relative length between the
nodes of each lever can be used to represent the ring-to-sun ratio of
each respective gearset. These lever ratios, in turn, are used to vary
the gear ratios of the transmission in order to achieve appropriate
ratios and ratio progression. Mechanical couplings or interconnections
between the nodes of the various planetary gear sets are illustrated by
thin, horizontal lines and torque transmitting devices such as clutches
and brakes are presented as interleaved fingers. If the device is a
brake, one set of the fingers is grounded. Further explanation of the
format, purpose and use of lever diagrams can be found in SAE Paper
810102, authored by Benford, Howard and Leising, Maurice, "The Lever
Analogy: A New Tool in Transmission Analysis", 1981, which is hereby
fully incorporated by reference.

[0036]The powertrain 10 includes an input member 17 continuously connected
with the engine 12, an output member 19 continuously connected with the
final drive mechanism 16, a first planetary gear set 20A having three
nodes: a first node 22A, a second node 26A and a third node 24A; a second
planetary gear set 30A having three nodes: a first node 32A, a second
node 36A and a third node 34A; a third planetary gear set 40A having
three nodes: a first node 42A, a second node 46A and a third node 44A.

[0037]The input member 17 is continuously connected with the node 32A. The
output member 19 is continuously connected with the node 44A. The node
22A is continuously connected with the transmission housing 60.

[0039]A first torque-transmitting device, such as brake 50 engages the
node 46A with the transmission housing 60. A second torque-transmitting
device, such as clutch 52, engages the node 26A with the node 46A. A
third torque-transmitting device, such as clutch 54, engages the node 26A
with the node 42A. A fourth torque-transmitting device, such as clutch
55, engages the nodes 24A and 36A via interconnecting member 70 with the
node 42A. A fifth torque-transmitting device, such as clutch 56, engages
the node 32A with the node 46A. A sixth torque-transmitting device, such
as clutch 57, engages the node 34A with the node 42A.

[0040]To establish ratios, three torque-transmitting devices are engaged
for each gear state. The engaged torque-transmitting devices are
represented by an "X" in each respective row of FIG. 1b. For example, to
establish reverse gear, the brake 50 and clutches 55 and 57 are engaged.
The brake 50 engages the node 46A with the transmission housing 60. The
clutch 55 engages the nodes 24A and 36A with the node 42A. The clutch 57
engages the node 34A with the node 42A. Likewise, the eight forward
ratios are achieved through different combinations of clutch engagement
as per FIG. 1b.

[0041]The powertrain 10 may share components with a hybrid vehicle, and
such a combination may be operable in a "charge-depleting mode". For
purposes of the present invention, a "charge-depleting mode" is a mode
wherein the vehicle is powered primarily by an electric motor/generator
such that a battery is depleted or nearly depleted when the vehicle
reaches its destination. In other words, during the charge-depleting
mode, the engine 12 is only operated to the extent necessary to ensure
that the battery is not depleted before the destination is reached. A
conventional hybrid vehicle operates in a "charge-sustaining mode",
wherein if the battery charge level drops below a predetermined level
(e.g., 25%) the engine is automatically run to recharge the battery.
Therefore, by operating in a charge-depleting mode, the hybrid vehicle
can conserve some or all of the fuel that would otherwise be expended to
maintain the 25% battery charge level in a conventional hybrid vehicle.
It should be appreciated that a hybrid vehicle powertrain is preferably
only operated in the charge-depleting mode if the battery can be
recharged after the destination is reached by plugging it into an energy
source.

[0042]While the best modes for carrying out the invention have been
described in detail, those familiar with the art to which this invention
relates will recognize various alternative designs and embodiments for
practicing the invention within the scope of the appended claims.